Advent of Code 2023 Day 18

— Day 18: Lavaduct Lagoon —

We need to dig a lagoon to hold some lava, according to some up/down/left/right directions.

The Elves are concerned the lagoon won’t be large enough; if they follow their dig plan, how many cubic meters of lava could it hold?

with open('data-2023-18.txt', 'r') as f:
    inp = f.read().splitlines()

Parse the input then fill in a numpy array to do the digging

# tracking
x = 0
y = 0
maxx = 0
maxy = 0
minx = 0
miny = 0


# moves for part 1
p1 = [x.split() for x in inp]

for p in p1:
    # number of moves
    n = int(p[1])
    # directions
    if p[0] == 'R': 
        x += n
    elif p[0] == 'L': 
        x -= n
    elif p[0] == 'D': 
        y += n
    elif p[0] == 'U': 
        y -= n
    # check on max
    if x > maxx: 
        maxx = x
    if y > maxy: 
        maxy = y
    if x < minx: 
        minx = x
    if y < miny: 
        miny = y
      
maxx, maxy, minx, miny

maxx - minx, maxy - miny

(387, 321)

Let’s use that for the array size

import numpy as np
import csv

lava = np.zeros((500, 500), dtype=int)

# tracking
x = 250
y = 250

lava[x,y] = 1

for p in p1:
    # number of moves
    n = int(p[1])
    # directions
    if p[0] == 'R': 
        for s in range(n):
            y += 1
            lava[x,y] = 1
    elif p[0] == 'L': 
        for s in range(n):
            y -= 1
            lava[x,y] = 1
    elif p[0] == 'D': 
        for s in range(n):
            x += 1
            lava[x,y] = 1
    elif p[0] == 'U': 
        for s in range(n):
            x -= 1
            lava[x,y] = 1

summer = 0
for l in lava[195:201]: 
    # print(''.join(str(l[0:500])))
    # print(sum(l))
    summer += sum(l)

# summer

np.savetxt('data-2023-18-out.csv', lava, delimiter=',', fmt='%d')

Doesn’t have to be a separate cell but feels like a different step in the procedure: loop through and add ones into the array for filled in lava lake.

for x, l in enumerate(lava): 
    # keep track of if we are on or off, always starts off
    dug = False
    lock = False
    for y, v in enumerate(l):
        if dug == False: 
            if lava[x,y] == 1 and lava[x,y+1] == 0:  
                # we are starting a dig out between trenches
                dug = True
                lock = False
            elif lava[x,y] == 1 and lava[x,y+1] == 1: 
                # we are on the edge of a trench
                dug = True
                lock = True
            elif v == 0: 
                # we are off and want to stay off
                pass
        else: 
            # dug == True
            if lock == False: 
                if lava[x,y] == 1 and lava[x,y+1] == 0: 
                    # the end of the trench, turn off digging
                    dug = False
                elif lava[x,y] == 1 and lava[x,y+1] == 1: 
                    # the end of the trench, turn off digging
                    lock = True                  
                else: 
                    # current value is 1 or 0, within 
                    lava[x,y] = 1
            else: 
                # lock = True, along the edge
                if lava[x,y] == 1 and lava[x,y+1] == 0:
                    # going into the space that needs to be dug
                    lock = False
                
                
summer = 0
for l in lava[195:201]: 
    # print(''.join(str(l[0:500])))
    # print(sum(l))
    summer += sum(l)

summer  

# 188696 too high  
# manual colouring in a spreadsheet
# 46338 too high
# 46334 correct

np.int64(1532)

— Part Two —

Oops, the instructions were wrong!

Convert the hexadecimal color codes into the correct instructions; if the Elves follow this new dig plan, how many cubic meters of lava could the lagoon hold?

# parse some hex digits
ph = [x.split()[2] for x in inp]

p2 = [x.replace('(', '').replace(')', '').replace('#', '') for x in ph]

def get_direct(h): 
    # The last hexadecimal digit encodes the direction to dig: 
    # 0 means R, 1 means D, 2 means L, and 3 means U.
    dirs = {'0': 'R', '1': 'D', '2': 'L', '3': 'U'}
    return dirs[h[-1]]
  
pd = [[get_direct(x), int(x[:5], 16)] for x in p2]